Experimental Information on the Adsorbed Phase of Water Formed in the Inner Pore of Single-Walled Carbon Nanotube Itself.

Thus far, nobody has successfully obtained the accurate information on the properties of the adsorbed phases of gases or vapors formed inside a cylindrical micropore of single-walled carbon nanotube (SWCNT) itself based on the experimental procedure. In this work, we succeeded in analyzing experimentally the properties of adsorbed nitrogen and water confined in the inner pore of SWCNT itself by opening the pore composed of close-ended SWCNT without any changes in the surface state and also by applying the unique method for characterization; both the amounts, as well as properties, of surface functional groups and the bundle structure are the same even after the treatments for introducing an open-ended structure to a close-ended one. As a result, the average pore sizes, as well as characteristic adsorption behavior, on the two types of sample were available from the analysis of respective difference adsorption isotherms of nitrogen measured at 77 K between the adsorbed amounts on the open-ended SWCNT and that on the close-ended one. The evaluated pore sizes well coincide with the results estimated by Raman data. These results strongly support that we could analyze the adsorbed phases formed only in the inner pore of SWCNTs by applying the present method. Furthermore, we could analyze the adsorbed phase of water formed inside the cylindrical micropore of SWCNTs, showing the difference in the densities of adsorbed water depending on the pore sizes from the value of bulk water; the densities of the adsorbed water were evaluated to be 0.62 and 0.71 g mL(-1) for SWCNTs having average pore sizes of 1.3 and 1.7 nm, respectively, which were in harmony with those obtained by the theoretical calculations reported by other researchers. The proposed analysis method makes it possible to recognize the focused states of the adsorbed water formed inside the cylindrical micropore of SWCNT more precisely and correctly. The method proposed will shed light on the discussion related to the detailed nature of various adsorbed gases into SWCNT, to the detailed role of adsorbed species formed inside pore in various phenomena, and to the designing the useful materials based on the gained knowledge.